package com.lingxi.d1_1;

import java.util.Scanner;

public class test
{
        public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            int a = sc.nextInt();
            int sum = 0;
            for (int i = 1; i <= 100; i++) {
                if (i % 3 == 0) {
                    sum += i;
                }
            }
            System.out.println(sum);
        }
}